Present data storage devices, such as tape and disk drives, provide limited feedback whenever an error occurs. The feedback is generally broad, indicating only the top-level cause of the error or the general area to which the error relates. For example, a data storage medium may be damaged or be of poor quality and consequently the data storage device may report that the signal-to-noise ratio is too low for the device to reliably read and write to the medium. Without knowing that the medium is damaged or of poor quality, the user might contemplate replacing the storage device. This is particularly true if the same error is reported by the storage device for various types of problems.
Additionally, the feedback provided by data storage devices is reactive and is reported to the user only after the error has occurred. Accordingly, the user is only made aware of the problem at a time when remedial measures are no longer possible.
U.S. Pat. No. 6,249,890 describes a disk drive that includes a controller for predicting future failure of the magneto-resistive head of the drive. The controller measures a characteristic of the head or readback signal and compares the characteristic against a baseline value. As the performance of the head deteriorates, the difference between the measured characteristic and baseline value increases. When the difference between the characteristic and the baseline value exceeds a predetermined threshold, the controller reports that future failure of the head is likely to occur.
Characteristics measured by the controller include the electrical resistance of the head, the nonlinearity of the head, the amplitude of the readback signal and the asymmetry of the readback signal. When measuring the amplitude or asymmetry of the readback signal, the head is positioned over a service track of the disk and reads test data in the form of a constant frequency data pattern. The controller then compares the amplitude or asymmetry of the test readback signal against that the same measurement made during the manufacture of the drive.
The disk drive controller of U.S. Pat. No. 6,249,890 only predicts potential problems with the head of the disk drive. The controller is unable to predict or even diagnose problems with the data medium. Additionally, when measuring the readback signal amplitude and asymmetry, the controller reads known test data stored on a service track of the disk and compares this against measurements made when the drive was manufactured. The controller is therefore dependent upon the same disk being used during the lifetime of the drive. Whilst this arrangement is suitable for fixed-media devices (e.g. hard disks), the controller is unable to predict potential problems for exchangeable-media devices (e.g. tape, CD and DVD drives) based upon readback signal measurements. Furthermore, the controller reports that a future failure of the head is likely when the readback signal amplitude drops below a threshold value. However, the same drop in readback signal amplitude may occur when the head becomes dirty. Accordingly, the user may be advised by the controller to replace the disk drive when the problem may be resolved merely by cleaning the head.